Service observing circuit



Sept 23, 19581 A. E. JOEL, JR., ErAL 2,853,562

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SERVICEQBSERVING CIRCUIT 11 Sheets-Sheet 2 Filed Dec. 28, 1955 EN NNNCNE /Nl/ENTORS Sept- 23, 1958 A. E. JOEL, JR., ETAL 2,853,562

SERVICE OBSERVING CIRCUIT l1 Sheets-Sheet 5 Filed DeG. 28. 1955 AITORNEY A. E. JOEL, JR., ETAL 2,853,562 SERVICE oBsERvING CIRCUIT sept. 23,195s 11 Sheets-Sheet 4\ Filed D69. 28, 1955 E wl .tm

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SERVICE oBsERvING CIRCUIT 11 Sheets-Sheet 5 FiledDeG. 28, 1955 ATTORNEYSept. 23, 1958 A. E. JOEL, JR., ETAL 2,853,562

SERVICE oBsERvING CIRCUIT In u N 1l Sheets-Sheet G A. E JOI-,J/a/NVENTORS M E KROM Filed DGO. 28, 1955 ,y ATTORNEY SePf- 2.3, 1958 A. E.JOEL, JR., ETAL 2,853,562

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A. f ELJR. M. iA/@0M /NVENTORS Sept. 23, 1958 Filed Dec. 28, 1955 11Sheets-Sheet 8 SERV/CE OBSERV/NG CONTROL C /RC Ul T SERV/CE OBSERV//VGC/RCU/T .1m-ma ATTORNEY Sept. 23, 1958 A. E; joEL, JR., ETAL 2,853,562

` SERVICE oBsERvINC CIRCUIT Filed Dec. 28, 1955`v 11 Sheets-Sheet 10 IA. EJOEL JR. /NVENTORS M E KRM By WTTI ,Qu QWNN ATTORNEY 11sheets-,sheet 11 Sept. 23, 1958 Filed Dec.

ATTORNEY nited State@ Patent Gi SERVICE oasnRvnsG CIRCUIT Amos E. Joel,Jr., South Orange, and Myron E. Krom, Convent Station, N. J., assgnorsto Beil Telephone Laboratories Incorporated, New York, N. Y., acorporation of New York Application December 28, 1955, Serial No.555,944

Claims. (Cl. 179-1752) This invention relates to telephone serviceobservation equipment and morev particularly to service observingcircuits for line concentrator telephone systems.

Service observation may be either routine observation or complaintobservation. Routine observation is utilized as a random check of thetelephone service provided to a group of telephone subscribers. Asampling of the calls originating at one of the subscriber lines may beutilized for .the routine observation. Complaint observation is utilizedwhen a telephone subscriber registers a complaint or inquiry concerningthe nature of the service provided. The substance of the complaintsembraces almost the entire range of telephone service and includes suchitems as wrong numbers, dont answer calls, over-v charges and variousother occurrences generally based upon some improper use of the callingdevice or faulty performance of the telephone line or central oiceequipment. For complaint observation it is advisable to determine froman actual observation of all the calls originating at the subscriberline whether poor service is being rendered and if so to determine thecause.

In order for a routine or a complaint observation operator to observe,monitor or supervise the operation of the switching equipment involvedin serving a subscriber' line responsive to the origination of a callthereon, the operator must receive an indication -of the origination ofa call on the line and must be provided with a bridging talkingconnection across the line. When the 'subscriber line terminates at oris connected directly to the central oice the provision of suchindication and connection is a relatively simple matter. However, inconcentrator telephone systems, for example, of the type described inthe Joel-Krom-Posin Patent No. 2,812,385, issued on No vember 5, 1957,the subscriber lines terminate in the line concentrators which are eachconnected by relatively few concentrator trunks to the central oflice.The central oice is therefore not directly in information,cornmunication with the subscriber lines due to the interposition oftheremote line concentrator.

It is a general object of this invention to provide line observationfacilities for routine and forcomplaint observation for subscriber linesin a line concentrator telephone system.

As described in the above-identified disclosure of Joel- Krom-Posin,line concentrator systems elfectV considerable savings in the cost ofoperation of the telephone plant by avoiding the necessity of providinga separate direct connection from the central office to each subscriberline. The greater the ratio of subscriber lines to concentrator trunks,without loss of telephone service, the greater are the savings. Afeature therefore of this invention relates to means for providingservice observation facilities in a line concentrator system withoututilizing a separate observation trunk. The service observation isprovided over existing concentrator trunks withoutinterfering withnormal telephone service. f

In the line concentrator system described in the above- 2,853,562Pateatel Sept. 23, s

ice-

identified disclosure of Joel-Krorn-Posin, the subscriber lines areconnected to the concentrator trunks on a random slip multiple basis:that is, each subscriber line is connectable to only some of theconcentrator trunks. The trunks that are connectable to a subscriberline are referred to as a trunk multiple. The term random slip indicatesthat the lines have access to different combinations of trunks or'thatthe trunks are different in different trunk multiples. In addition tothe random slip trunk multiplying, a preference is provided for theselection of the trunks in each slip multiple. The preference selectiondistributes the calling load because a trunk which is common to morethan one multiple may have a different preference in each multiple, v

In an illustrative embodiment of this invention, when routineobservation is provided for a subscriber line, a service observationcontrol at the central oiiice is set to register the identity of thesubscriber line and an observation switch is set to connect thepreferred trunk of the line' to an o-bservation circuit. When a call isoriginated at the subscriber line and the preferred trunk is selectedfor the dial-tone connection, an indication is provided by the serviceobserving control to an observation operator at the observation circuit.When the observation operator receives the service observationindication, a connection is made at the observation line circuit to thepreferred trunk. In this manner a bridging connection is provided at thecentral oflice to the preferred trunk. Routine observation is thereforeprovided without the necessity of a separate bridging or observationtrunk between the concentrator and the centraly oflice. AOnly a samplingof originating calls may be observed because the preferred trunk must beselected in order for the provision of an indication to the observationoperator. By observing only on preferred trunk calls, the switchconnecting the observation trunk to the concentrator trunk mayeffectively be merely a jumper.

Still another feature of this inventionl relates to complaintobservation means which enablesthe observation of a line for all callsoriginating thereat; For complaint observation, the observation switchis an automatically operating circuit for establishing a connection fromthe observation trunk to any one of the concentrator trunks.

It is not set to preselect any one of the concentrator trunks. When aconcentrator trunk is selected, the observation switching circuitreadies a connection from the observation trunk to the selected trunk.When the call is from the observed line, the observation controlprovides an indication to the operator at the observation circuit andoperates the switching circuit to complete the path from the observationtrunk to the selected trunk. In this manner all calls from a subscriberline may be ob served independently of which of the concentrator trunksis utilized.

Still another feature pertains to means effective when a call isoriginated at a predetermined subscriber line for providing anobservation indication before the initiation of a trunk selectingsequence of operation. The indication is provided as soon as the lineidentity'is registered at the central office.

Still another feature of this invention vrelates to means. for providingservice observation for any one of the lines that is connected to anyone of a plurality of concentrators.

In line concentrator systems, in addition to routine and complaintobservation, it is also advisable to provide concentrator trunkobservation. Still another feature of this invention relates thereforeto means for observing all the calls originating at the concentrator andwhich utilize a predetermined one of the concentrator trunks. Theservice observing circuit is connected by the observadescribed.

tion switch or a jumper to the concentrator trunk, and

the concentrator trunk. When the. concentrator trunk is selected forconnection to any calling line, an indication is provided to theobservation operator.

Further'objects and features will become` apparentto those skilled inthe art upon consideration ofthe follow.`r ing description read inconjunction with the drawingsf wherein Figs. 1 through 8, arranged inaccordance with Fig..9,-.:"

provide a circuit representationv of the line concentrator and serviceobservation system ofthe presentinvention:

wherein:

Figs. 1 and 4 show. a circuit representation of` thelineconcentrator;and

Figs. 2, 3 and 5 through 8 show, a circuitrrepresentaf tion ofthecentral .oflce;

Fig. 9 illustratesthe arrangement of Figs.. l through: 8;-

Fig. 10 is a table illustrating the-slipjrnultiple. connetions and thetrunk preference foreach multipleg- Figs. 11 andl2 are tablesillustrating the connectionsl of the armatures'offrelays 6VGO-11 whichare shownin.

Fig. 6;

Fig. 13 is a circuit representation of the'switching circuit whichfisutilized for complaintobservation; and.

indicate the function thereof. Relay ZHGG, for example, i

is the horizontal ,group relay 0 and appears in Fig. 2. Beforeproceeding with a description of they service observation system of thisinvention, the line concentrator normal scanning sequence -of operationsis briefly-:.

Serial No. 555,916, filed oneven date herewith. The scanning system visbriey described herein because it is utilized, as is hereinafterdescribed, during the establishmentrof ,a dial-tone connection for anyone of the subscribervlines.

Normal scanning The line concentrator 110` shown in Figs; 1 and 4 isV ata distance therefrom in order to conserve outside plant The scanning`system is described in detail, in the copending., application byAlmquist-Ioel-Posin;

The liney concentrator 110 providesv a facilities. The line concentrator110 is connected to the Y central otiice by ten trunks lSTO-9 and threecontrol pairs lCP1-3, The trunks 5T09 provide talking paths-betweentheline concentrator 110 and theV central-office and the three controlpairs 1CP1-3 provide for signaling paths to and from the central officeequipment. vWith'" all 600 subscriber lines idle, the central.oicecontinu# ouslyy and synchronously scans the ten groupsof 60subscriber lines.

The ten line concentrators 110-19 are synchronously scanned undercontrol of a scanner pulse generator-ZPS,

concentrators 11G-19l and also, to a concentrator originating callregister 300.

Thescanner pulse lgenerator v 2PG and the concentrator originating callregister 300 are common control Vequipment for all ten concentratorsl10n-19. Theten line,concentrators 110,-19 v and the.,

register 300 are synchronously and cyclically operated under controlofthe scanning pulses from the generatorl ZPG.

. The scanner pulse generator ZPG supplies :four types of pulses:vetrical group pulses, vertical le pulses, reset pulses and mark pulses.As in the ordinary crossbar telephone system, the subscriberA lines arearbitrarily arranged in vertical groups, vertical tiles and horizontalgroups. Such crossbar systemsare described, for example, in-,the Patent2,585,904 which ,was granted to A. I. Busch, February 19, 1952. All .thesubscriber lines connected to one o-f the' ten concentrators 110-19 arein the same horizontal group and theyare subdivided into twelve verticalgroups, each of` which .includesiive verti cal files. The vertical grouppulses supplied by the scanner pulse generator 2P.G selecta group of velines connected to each of the line concentrators -19. The verticalgroup pulse is supplied simultaneously to the ten line concentrators110r19lso that 5 times 10,. .or '50, .subscriber lines are selected;Between-.two such .vertical group pulses, the-scannerV pulsegeneratorZPG supplies v ive vertical tile .pulses to the concentrators110.-19,'.as

shown in Fig. 14 which illustrates the normal scanning' pulse sequence.One subscriber line :connected to each of theconcentrators, or ten inall,.is scanned by each vertical yiile pulse. In order to scan the 600lines, the scannerrvpulse generator ZPG provides to each of the ten lineco-ncentrators v110-19and to the register 300,

twelve. l5volt vertical .group pulses spaced at intervalsv of 10milliseconds'and five 15-.volt vertical file pulses spaced atintervalso-f 2 milliseconds between each pair ofvertical group pulses.The vertical le. andzvertical. group pulses are 1/2millisecondrpulses,andthe complete scanning Ycycle has a duration ofmilliseconds.

In addition to the vertical group-and the vertical le pulses, thegenerator 2PG' supplies one reset pulse at the beginning of the cycle toensurev the synchronous operation of the line concentrator-.scanningcycles and the originating call register cycle with that of thegenerator ZPG. The reset pulse, as is hereinafter described, alsofunctions as the rst vertical file pulse so that only 59 vertical filepulses are provided instead of 60 for a single cycle.

To v-recapitulate, during one ,scanningrcyclathe .pulsen generator 2PGsupplies one'resettpulse, twelve vertical group pulses and 59 verticalle; pulses. kOne vertical file Vpulse is provided, if theA reset` pulseis counted as a vertical le pulse, for each of the 60 subscriber lines.

The scanner pulse generator ZPG alsoprovides mark pulses which areutilizedas-is hereinafter-described,

when a call to or froml one of the..6001subscr iber lines is beingserviced.

The originatingl register 300v hasv two* ring., counters 3VFR and 3VGR.The counter 3VFR is a five-stage circuit which advances one stepgforeachuginput pulse supplied thereto. AThe.vertical'le',pulses'fromhegenerator 2PG are supplied through the .counter input ter-` minal P tothe input terminal 3 of each of thesivel stages 3VFRO-4. A singlecounter stage, such as thei'stage 3VFRO, ymay be thought of as acombination of an enabling'gate and flip-flop circuit. A stage, is saidto be gated when its gate is enabledandis said to be on when itsflipfflop circuit is set. A stage may be turned on Aonly Vif its gate-isenabled to allow the input pulse through to set, or turn on, itsip-op-circuit. When a stage is turned on the potential: at its outputYterminal'2 changes from -20 volts to -2 volts to enable the gate of thesucceeding stage. Assumefory example, that at the beginningA ofthescanning Ycycle the stage SVFRG hasv its ip-op circuit-set. Only :oneof vthe stages 3VFRO-4 is set at anytime, f, andthe stage succeeding theset `stage is the only ygated. `or enabledstage.fxThei i11,

in a hook arrangement to function as a point contact transistor. Sucharrangements are described, for eX- ample, in the Patent 2,655,609 whichwas granted t W. Shockley on October 13, 1953. The emitter electrode oftransistor ST1 isconnected to ground through the resistor SR1 andthrough the varistor 3D2. The resistor SR1 functions as a load resistorfor the input pulse and the varistor 3D2 provides a low resistance pathfor the emitter sustaining current, and also functions to dissipate anynegative pulses to ground. The base of transistor ST1 is connected tothe collector of transistor ST2, to the volt direct-current potentialsource SB1 through the base resistor SR4 and through the reset terminal4 to the terminal 5 of the succeeding stage SVFRL The emitter electrodeof transistor ST2 is connected to the output terminal 2 and to the -20volt battery SBZ through resistor SR6.

With the iirst stage SVFRO on, the output terminal 2 thereof is at apotential of -2 volts due to the current through the resistor SR6. Withthe -2 volt potential at terminal 2 of stage SVFRO, the varistor SDS ofstage SVFRI is relatively forward-biased or only slightly backbiased.The terminal 2 of stage SVFRO is connected through the terminal 1 ofstage SVFRI and resistor SRS to the varistor SDS. With the varistor SDSin stage SVFRI relatively forward-biased, the stage SVFRl is enabled sothat an input pulse through terminal S thereof causes it to turn on. Ifstage SVFRO is not on and its terminal 2 is at a potential of -20 volts,varistor SDS in stage SVFRI is reversed-biased so that an input pulsethrough its terminal does not turn it on.

When the first pulse is supplied to the terminals S of stages SVFRO-4from the generator 2PG, it turns on the stage SVFRI through its enabledgate circuit, which includes the forward-biased varistor SDS. Thepotential at terminal 2 of stage SVFRl changes from 20 volts to -2 voltsto enable the stage SVFR2 and reset the stage SVFR. The terminal 2 instage SVFRl is connected through the capacitor SC2 of stage SVFR1,varistor SD4 and terminal 5 to terminal 4 of stage SVFRO. Terminal 4 isconnected, as described above, to the base electrode of transistor ST1.When terminal 2 of stage SVFRl changes in potential from 20 volts to -2volts, the change in potential is provided to the base of transistor ST1in stageSVFRt) causing the stage SVFRO to turn ott. When the stage SVFROis turned off, in this manner, the potential at its terminal 2 decreasesfrom -2 volts to -20 volts disabling the gate circuit including thevaristor SDS in the stage SVFRL To briefly recapitulate, the irst pulsesuppliedto terminals 1 of stages SVFRO-4 turns onl the stage SVFRI whichenables the stage SVFR2 and resets or turns olf the stage SVFRG. Whenthe stage SVFRO is turned ott, it disables the stage SVFRI. After therst pulse, therefore, the stage SVFRl is turned on and the others areturned olf, and the stage SVFR2 is enabled and the others disabled.

The second pulse from the generator 2PG turns on `the stage SVFRZ, whichenables the stage SVFRS, and

turns off the stage SVFRl. The stage SVFRS, in turn, disables the stageSVFR2. The pulses supplied to the terminals S of the stages SVFRO-4 inthis manner advance the setting from stage to stage with the sixth pulsebeing equivalent to pulse No. l. The sixth pulse is equivalent t o thefirst pulse because the stages SVFRO-4 are connected in a ring with theoutput terminal 2 of stage SVFR4 being connected to terminal 1 of stageSVFRO and the terminal 5 of stage SVFRU being con nected to the resetterminal 4 of stage SVFR4.

The above sequence continues from stage to stage in the counter SVFRuntil the pulse generator 2PG is disabled. A similar sequence of eventstakes place in the counter SVGR except that it takes twelve pulses tocomplete a cycle instead of tive since the counter SVGR has twelvestages.

At the beginning of each scanning cycle a positive reset pulse issupplied from the'pulse generator 2PG to the register S00. The resetpulse is supplied, respectively, through thereset terminal R, and theserially connected varistor 3D1 and resistor SR to the terminal 6 ofstage SVFR@ and also to the reset terminal R of counter SVGR. When a.reset pulse is applied to terminal 6 of stage SVFRO it turns the stageon since terminal 6 is connected to the emitter electrode of transistorST1. Terminal R is also connected through the varistors SD7 to the resettreminals 4 of the other stages in the counters SVFR and SVGR to resetor turn off these stages. At the beginning of each cycle, therefore, thepulse generator 2PG supplies a reset pulse to the counters SVFR and SVGRto return them to normal with only the first stage in each counter set.As shown in Fig. 14, the generator 2PG does not supply a vertical filepulse when the reset pulse is supplied. Thereset pulse functions as thefirst vertical tile pulse since it is supplied to the input terminal 6of stage SVFRO and advances the vertical file counter SVFR from stageSVFR4 to stage SVFRt). The generator 2PG therefore supplies twelvevertical group pulses, one reset pulse and 59, not 60, vertical tilepulses to the register SG() during one scanning cycle.

The pulse generator 2PG supplies the vertical tile, vertical group andreset pulses to the counters SVFR and SVGR, as described above, and alsothrough the sets of control leads 1CP1-S to the concentrators 11049.

The vertical file pulses are supplied from the generator 2PG throughamplifier 2VFL and resistor 2K8 to the upper primary of transformer 2T1which, in turn, is connected to -20 volt battery 2B5 and to the varistorZV1. The secondary of transformer 2T1 is connected through the controlpair lCPS to the concentrator 110. The vertical group pulses aresupplied from the generator 2PG through the amplifier ZVGL, resistor2R10 and the upper primary of transformer. 2 T2. The upper primary oftransformer 2T2 is also connected to the -20 Volt battery 2B6 and tovaristor 2VS. The secondary of transformer 2T2 is connected through thecontrol pair 1CP2 to the concentrator 110. The reset pulses are suppliedthrough amplifier 2RSL, and resistor 2R11 to the lower primary oftransformer 2'1'2 which is shunted by varistor 2V4.

During the normal scanning cycle, the scanner pulse generator 2PGcontinuously and cyclically provides the vertical group, vertical tileand reset pulses to the line concentrator originating call register S00and to the ten concentrators -19. The concentrators 11B-19 each includesa vertical group ring counter lVG and a vertical tile ring counter 1VFwhich are cyclically and synchronously operated with the ring countersSVGR and SVFR. The counters 1VG and IVF are similar to the counters SVGRand SVFR. The vertical file, vertical group and reset pulses aresupplied through the ten sets of three control pairs lCPl-S with eachset of three control pairs lCPl-S being connected to one of the lineconcentrators 110-19. The line concentrator 110, shown in Figs. 1 and 4,is connected through one set of the control pairs 1CP1-S to thetransformers 2T1-S. The vertical group, vertical file and reset pulses,provided in this manner to each of the ten line concentrators 110-19,cyclically and synchronously operate the ring counters IVG and lVF ineach of the ten concentrators 110-19.

At the line concentrator 110 the control pairs lCPl-S are connected,respectively, to the secondaries of the transformers 1T4-6. The lowerprimary of the transformer 1T6, which is shunted by the resistor 1R1, isconnected through resistor 1R2 to the vertical file receiving amplierIVFA. The upper primary winding of the transformer ITS, which isshuntedby the resistor 1R6, is connected through resistor 1R4 vto thevertical group receiving amplifier IVGA. The lower primary Winding ofthe transformer ITS is connected through the resistor IRS to the resetamplifier IRS.

The amplified vertical file pulses are supplied from the amplifierIVFAto the input terminal P of the five-stage vertical file ring counterIVF. T he vertical group pulses are supplied from the amplifier IV GA tothe input terminal P of the vertical group ring counter IVG. Theamplified reset pulse from the amplifier IRS is supplied through thecapacitor 1C2 to the reset terminals R of the counters IVF and IVG. Thecapacitor 1C2 is connected to the grounded resistor 1R10 which providesa recharge path for the capacitor' IC2. The counters IVF and IVG arestepped, in the manner, by the vertical group and vertical file pulsesin synchronism with the counters SVFR and SVGR .undercontrol kof the,generator ZPG.

Capacitor ICZis also connected through varistor ID7 to the resetterminal3 of the fiip-ffop circuit IM which is similar to thehereinafter described flip-flop .circuit ZHGT. Briefly, the circuit IMis a bistable device which is set when an input pulse is provided toterminal I and reset when a pulse isprovided to terminal 3. Terminal 3is connected to ground through resistor 1R9. The reset pulse insuresthat the flip-Hop circuit IM is reset at the beginning of each scanningcycle.

As long vas there are no service requests from any of the 60 subscriberlines 4L00-59, or a terminating call thereto, eleven sets of counters,one in the central ofiice register 300 and one in each of the lineconcentrators 110-19, synchronously step through the count of 60, with'a reset pulse being supplied at the beginning of each cycle to insurethe synchronism of the sets of counters.

At each combination of operated counter stages in counters IVG and IVF,a pulse is directed to scan one of the 60 lines 4L00-59 by the linescanning units 4SC00- 59'. Only line 4L04 and unit 4SC04 are shown inthe line con-centrator 110. Each of the line scanning units 4SC00459 hastwo gating circuit components, one controlled by the counters IVF andIVG and the other controlled by the condition of the associated line.yThe first gating circuit component which includes the varistor 4Dfunctions as an enabling or readying component for the scanning unit.

The ring counter IVG functions to successively ready groups of five linescanner units at a time, by changing the reverse-bias across thevaristor 4D from y--20 volts to -2 volts. When the first stage incounter IVG, for example, is set, a relatively positive potential isprovided from the first output terminal 2 thereof, through resistors 4VGof the five line scanner units 4SC00-4 to the respective varistors 4D.The five varistors 4D in the units 4SC00-4 become biased to allow thepassage of pulses from the ring counter IVF through capacitors 4VF. Thevaristors 4D in the other 55 units 4SC05-59 are reversed-biased by the-20 volt potential at terminals 2 of the other eleven stages of counterIVG.

The ring counter IVF provides scanning pulses successively to twelveline scanning units at a time. When the fourth, or last, stage forexample, is set, a positive pulse is provided from the terminal v2thereof to the capacitors 4VF in the units 4SCO4, 4SC09, 4SCI4, 4SCI9,4SC24, 4SC29, 4SC34, 4SC39, 4SC44, 4SC49, 4SC54 and 4SC59. Of these,only the unit 4SC04, however, has been readied at this time by the ringcounter IVG. The positive pulse from terminal 2 of the last stage ofcounter IVF, therefore, passes through the capacitor 4VF of the unit4SC04, varistor 4D and capacitor 4C to the varistor 4S. The varistor 4Sis part of the second gating circuit component which is controlled bythe line condition.

In the unit 4SC04 the line 4L04 has associated therewith a resistor 4GS,which is connected from the tip lead T to the +5 volt battery 4B1, and aresistor 4ES fil which is connected from the ring lead R to the -20 voltbattery 4B2. If theusubscriber line 4L04 is open, the l-20 volt battery4B2 functions to reverse-bias the varistor 4S so that the. scanningpulse from the ring counter IVF is not transmitted through the varistor4S.v When, however, the subscriber line 4L04 is in a calling conditionwith the line closed, a circuit is completed from battery 4B1 throughresistor 4GS, substation 4S04 and resistor 4ES to battery 4B2. Thepotential at the junction between varistor 4S and capacitor 4C becomessufficiently positive to allow the scanning pulse from the last stage ofthe ring counter IVF to pass through the varistor 4S, amplifier 4SR, andresistor 1R7 to the lower primary of transformer IT4. Negativepotentials are suppressed bythe varistor,4D6 which is paralleled byresistor 4R7. l n l l The scanning units 4SC00-59, in this manner, allowthe vertical file pulses to pass through as a service request pulse whenboth gating circuit components are enabled.v The first component, whichincludes varistor 4D, is enabled by the counter IVG, and the secondcomponent, which includes varistor 4S, is enabled when the associatedline is closed. However, when the line 4L04 is connected to one of theYtrunks STG-9 and is therefore in a' busy condition, the varistor 4S, asis hereinafter described, is reverse-biased.

If all the lines 41.00-59 remain idle, the scanningsequence continuesunder control of the three sets of pulses, the vertical group, thevertical file andthel reset pulses from the central office. Eachvertical group pulse readies five line scanning units, and each verticalfile pulse scans one of the: five readied line scanning units. In thismanner thefive readied line scanning units are successively scanned bythe five vertical file pulses which.

occur between two of the vertical group pulses. At the time positionforthe first vertical fille pulse the vertical file pulseis actuallyomitted, as described above, and a reset pulse is transmitted from thecentral office to insure that the counters IVG and IVF are in the startposition. The first stage however, when reset, supplies a scanning pulseto the scanning unit 4SC00.

Routine service observation in response to a service request Whenroutine service observation is to be provided on one of the subscriberlines 4LG'0-59, the service observationcontrol S10 is set to registertheidentity of the line to be observed. If line 4L04 of concentrator 110is to be observed, the switch SHG is set at terminal 0, the switch SVFis set at terminal 4, the switch SVG is set at terminal 0 and the trunkselector switches SA-I are set at terminals L. When the switches SA-Iare set at terminals L, service observation is provided on a particularline and when the switches SA-I are at any other terminal, serviceobservation is provided, as is hereinafter described, for a particulartrunk. The switch SHG identifies the co-ncentrator to which the observedline or the observed trunk is connected. With switch SVF setat terminal4, switch SVG set at terminal 0 and the switches SA-l set at terminalsL, when a call is initiated from lineV 4L04 and its preferred trunk STOis utilized, an indication is provided to the service observing circuit801.

In addition to setting the switches SA-I, SHG, SVF and SVG, the serviceobserving switches 501 and 502 are set to connect the trunk 8T to theconcentrator trunk that is preferred for line 4L04. The switch 502selects one of the ten switches SCROf-9 which is individually associatedwith the ten concentrators liti-19 and switch 501 selects one of thetrunks 5T09 connected vto the selected concentrator. As is hereinafterdescribed, a preference is established for the selection of each set oftrunks STO-9. For line 4L04, for example, trunk STO is the preferredtrunk. The switch 501 is therefore set to connect trunk 8T to trunk STO.The switchesY 501 and $02 may comprise patch cords, relays, selectorswitches or the like to provide for the connection from trunk 8T totrunk STO.. Service observation is provided, in this mannner, fororiginating calls from line 4L04 only when trunk STO is utilized. Thisrandom sampling of originating calls is utilized for the routineobservation of the service provided to line 4L04.

When a call is initiated at yone of the substations 4S00-59, thevertical le pulse from the ring counter IVF is transformed by thescanning units 4SC00-59 to a service request pulse and supplied throughthe amplifier 4SR to the lower primary winding of transformer 1T4. Thelower primary Winding of transformer 1T4 is shunted by the varistor 1D3,and connected to the -20 volt battery 1B3. The secondary of thetransformer 1T4 is connected through the control pair 1CP1 to thetransformer 2T3 in the central office. The lower primary windin-g oftransformer 2T3 is connected through the receiving amplifier 2SRL andthe gate 2SRS to the input terminal 1 of the ip-tlop circuit ZHGTO.

The gate 2SRS is an inhibiting gate which normally allows pulsesthrough'from its terminal 1 to its terminal 2. The inhibiting gate 2SRShas three terminals 1-3, with terminal 1 being the input terminal,terminal 2 the output terminal and terminal 3 the control terminal. With-20 volts at its control terminal 3, the gate 2SRS functions to allowthe passage of pulses from its input terminal 1 through to its outputterminal 2. The -20 volt potential at terminal 3 relativelyforward-biases the varistor 2D4 which is connected thereto through theresistor 2R13. The varistor 2D4 is connected to the terminal 2 andthrough the capacitor 2C3 to terminal 1, and the junction betweencapacitor 2C3 and varistor 2D4 is connected through the resistor 2R14 tothe -20 volt battery 2B8. The forward-biased varistor 2D4 allows thepositive pulse from the amplifier ZSRL to appear across the resistor2R13. In its inhibiting state the terminal 3 is at a potential of -2volts and the varisto-r 2D4 is reversed-biased with a potential ofapproximately 1S volts. The presence of a positive lS-volt pulse acrossthe input resistor 2R14 is insufficient to overcome the reversebiasingof varistor 2D4 so that an output pulse ,does not appear across theresisto-r 2R31. Terminal 3 of the gate 2SRS is connected to the outputterminal 2 of the flipop circuit ZHGT which provides, as is hereinafterdescribed, the -20 Vol-t normal potential and the -2 volt inhibitingpotential.

The flip-dop circuit 2HGTO is a bistable transistor trigger circuithaving two transistors 2T4 and 2T5 connected in a hook arrangement. Anelectrical pulse applied to the input terminal 1 triggers the circuitfrom one state to the other and leaves it there until a reset pulse toits terminal 3 triggers it back again to its former state. The flip-flopcircuit ZHGTG is normal or o when its output terminal 2 is at apotential of -20 volts and oit-normal, or on, when it has received apositive pulse through its input, or set, terminal 1 to change thepotential at its output terminal 2 to -2 volts. A positive pulse throughthe reset terminal 3 restores the potential at its output terminal 2 to-20 volts. The time consumed in changing the output potential from onevalue to another is approximately 2/10 of a microsecond.

When the flip-flop circuit 2HGTO is in its oif condition, a very smallamount of current somewhat less than 10 microamperes is supplied fromthe +5 volt source ZBZ through resistor 2R2, transistor 2T4 and resistor2R1 to ground. The transistor 2T4 represents almost all of the impedancein this circuit path. With a 5-volt potential across the transistor 2T4its emitter is back-biased so that the transistors 2T4 and 2T5 are intheir low current quiescent condition. There is also a small currentbetween the source 2B2 and a *20 volt source 2B1. This path is fromsource 2B2 through resistor 2R2, the base-to-collector path throughtransistor 2T4, the base-toemitter path of transistor ZTS in parallelwith the collector-to-emitte path of transistor ZTS, through resistor2R4 to battery 2B1. With transistor 2T5 being in its off, or low currentquiescent condition, most ofthe potential drop is across it so thatterminal 2 is at a potential of -20 volts.

A When a positive pulse is supplied to terminal 1 of sufcient magnitudeto raise the potential of the emitter electrode of transistor 2T4 abovethat of its base electrode, the transistor 2T4 becomes conductive. Theinput terminal 1 is connected through the capacitor 2C1 to the emitterelectrode of transistor 2T4 and to ground through the resistor 2R1 andalso through the varistor 2D3. -When the transistors 2T4 and 2T5 areturned on, there is a low resistance path from ground through thevaristor ZDB, the emitter-to-collector path of transistor 2T4, thebase-to-emitter path of transistor ZTS and resistor '2K4 to battery 2B1.The increase in current through the resistor 2K4 causes an l8-volt dropacross it to change the potential at terminal 2 to -2 volts.` Thevoltage drop across the collector-to-emitter path of transistor ZTS isvery small so that the collector electrode thereof is effectively at the-2 volt potential. With the emitter electrode of transistor 2T5effectively at ground potential it is therefore 2 volts more positivethan its base electrode. This condition holds the transistors 2T4 andZTS on to provide for the bistable operation. The circuit 2HGTO includesa varistor 2D2 which is connected from the emitter electrode oftransistor 2T5 to ground. The varistor 2D2 prevents the output terminal2 from going positive or above ground potential.

The circuit 2HGTO remains in this stable condition until a positivepulse is received through the reset terminal 3. The reset terminal 3 isconnected through the capacitor 2C2 and varistor 2D] to the baseelectrode of transistor 2T4. The junction between capacitor 2C2 andvaristor 2D1 is connected to ground through the resistor 2K3. Thepositive pulse to the base lelectrode of transistor 2T4 makes it morepositive than its emitter electrode and thereby turns off the flip-flopcircuit ZHGTG.

The ip-op circuit 2HGTO is individually associated with the concentrator110. The line concentrator system also includes nine other lip-flopcircuits 2HGT1-9, not shown, which are individually associated with thenine concentrators 11119.

When the flip-flop circuit 2HGTt) operates, it functions generally tostop the transmission of the scanning pulses to the concentrators11G-19, to close the gate 2SRS and to call in a marker 799. The marker760 and the connectors 701 and 702 associated therewith are of the typedescribed in the above-identified Busch patent. The change from -20volts to -2 Volts at the output terminal 2 of the flip-flop circuitZHGTO functions as a stop potential to the generator ZPG, causes theinhibiting gate 2SRS to close, and causes the operation of the relay2HGO.

When the pulse generator ZPG stops, the ring counters 3VFR and SVGremain set at the calling line identity. For a service request from line4L04, for example, the counter 3VFR has stage 3VFR4 turned on and thecounter 3VGR has the rst stage turned on.

When gate 2SRS is closed, the central otlice becomes insensitive toservice requests, and remains in this condition until circuit ZHGTO isreset.

Terminal 2 of circuit 2HGTO is connected to the winding of relay 2HGOwhich is also connected to battery 2B3. When relay 2HGO operates, itconnects the -20 volt battery 2B3 through its operated armature 1 to oneside of the windings of relays 3VFTO-4 and 3VGTtl-11. The windings` ofrelays 3VFTO-4 are connected, respectively, through the varistors 3VO-4to the output terminals 2 of the counter stages 3VFRO-4, and thewindings of the relays 3VGTO-11 are connected, respectively, through thevaristors 3BG-11 to the output terminals 2 of the twelve stages incounter SVGR. With the counters 3VFR and SVGR stopped on the linelocation of the "1,1 calling subscriber, a -2 voltpotential is on theother side of one of the relays 3VFTO-4, and one of the relays 3VGTO11,causing them to operate. With a service request from line 4L04, relays3VFT4 and 3VGTO are operated.

When relay 2HGO operates, it also provides an indication of the identityof the line concentrator requesting service. The line concentratoridentity is, as described above, the horizontal group indication whichis zero for concentrator 110. Relay 2HGO operates and connects groundthrough its operated armature 2 and cable 2C5 to the line link markerconnector 702. When relay 3VFT4 operates, it readies a path forsupplying the vertical file information to the marker 700. When relay3VGTO operates, it provides an indication of the vertical group identityto the marker connector 702 by connecting ground through cable 3C5 tothe marker connector 702. The vertical group identity indication alsofunctions as a start signal for the marker 700.

When relays 3VFT4 and 3VGTO operate, they also ready a signal paththrough the service observation control circuit 810. With relays 3VFT4and 3VGTO operated, a connection is provided from the service observingcircuit 801 through the ring lead of the observation trunk 8T, lead 802,the armature of switch 8HG, terminal of switch SHG, cable .8C3, armature3 of relay 2HGO, the operated right armature of relay 3VGTO, cable 8C1,terminal 0 of the switch SVG, the armatures of switches SVG and 8VF,terminal 4 of switch SVF,

cable 8C2, the operated right armature of relay 3VFT4,

terminal L and the armature of switch 8A to the armature 0 of the trunkselector relay 7TSO. The trunk selector relay 7TSO, is operated, as ishereinafter described, during the trunk selectio-n sequence after themarker 700 seizes the line link connector 701. When relay 7TSO isoperated, a connection is provided from the grounded service observationresistor 7S0 to the service observing circuit-801 as an indication ofthe origination of a call at the observed line 4L04. The serviceobservation indication is provided to the service observing circuit 801before a connection is established through the concentrator 110 to thecalling linek 4L04.

When the marker 700 receives the start signal from the connector 702, itseizes the line link connector 701. The line link connector 701initiates an outpulsing operation, and a trunk selection operation, inorder to establish a connection'from the calling line 4L04 to a selectedone of trunks 5T0-9.

When the line link connector 701 is seized by the marker 700, itoperates one of the horizontal group relays 6H0-9, the dial-tone relay7D, and one of the vertical group relays 6VGO-11. In the exampledescribed above, when a call is initiated at line 4L04 and concentrator110, the relays 6H0, 7D and 6VGO are operated.

When the call is a terminating or call-back call instead ofankoriginating call, a similar sequence occurs for the selection of atrunk except that a terminating or call-back relay, not shown, isoperated instead of relay 7D.

When relay 6H0 is operated, it connects ground from the operated leftarmature of relay 3VFT4, throughcable 6C0, the operated armature F4 ofrelay 6H0 and cable 6C1 to the line link connector 701. In this mannerwhen relay 6H0 is operated, it supplies the vertical le informationthrough the connector 701 to marker 700. After the marker` 700 receivesthe vertical file information, it operates the corresponding one of therelays 7VFO-4 which is relay 7VF4 when the call is from line 4L04. Whenrelay 7VF4 is operated, ground is lconnected through the operatedarmature 2 of relay 7D, the operated armature 1 of relay 7VF4, theoperated armature 13 of relay 6VGO, the operated armature 22 of relay6H0 to the outpulse terminal of the pulse generator ZPG.

When the Voutpulse terminal is grounded upon the operation of relay7VF4, the generator 2PG supplies a reset pulse and the correct number ofvertical le and vertical group pulses to set the ring counters IVG and1VF at the identity of the calling line. Before sending the lastvertical le pulse, the generator ZPG opens the gate SLBT to permit aline busy test. The control terminal 3 of the gate SLBT is connected tobattery 5B4 through the resistor 5R8. The battery 5B4 normally providesa -20 volt inhibiting potential to the gate SLBT. When the enablingconnection is provided to the con# trol terminal 3 by generator ZPG, thegate SLBT is opened and the central oice becomes receptive to line busypulses from the concentrator 110.

The gate SLBT is a three-terminal device with an input terminal 1, anoutput terminal 2 and a control termi# nal 3. Normally with 2O volts atterminal 3, the gate SLBT functions to prevent the passage of pulsesfrom terminal 1 to terminal 2. Terminal 3 is connected to the varistor5V3 through resistor 5R6 and varistor 5V3 is connected to terminal 1through capacitor 5C4 and also to terminal 2. Terminal 2 is connected toground through resistor 5R7. With -20 volts at terminal 3, varistor 5V3is reverse-biased. nected to terminal 3, varistor 5V3 becomessufficiently forward-biased to allow the passage of line busy pulsesfro-m the concentrator 110.

When relay 7D is operated, it, in turn, causes the operation of thetrunk connect relay 6TC. The operating path for relay 6TC is frombattery 7B2 through the operated armature 1 of relay 7D andthe seriallyconnected normal armatures 1 of the six trunk selecting relays 7TSO-5 tothe winding of relay 6TC. When relay 6TC operates, it generally causesthe operation of all six preference relays 7TSO5. The windings of relay7TS4 and 7TS5 are connected directly to the armatures 9 and 10 of relay6TC, and the windings of relays 7TSO-3 are connected, respectively,through the operated armatures 1,y

2, 8 and 7 of relay 6VGO to armatures 1, 2, 8 and 7 of relay 6TC. Whenrelay 6TC operates, it extends, respec tively, the paths from thewindings o-f relays 7TSO-5 through the operated armatures 1, 2, 8, 7, 9and- 10 of relay 6H0, the normal armatures 1 of relays 5SRO, SSRI, 5SR7,5SR6, SSRS and 5SR9, and resistors 5R10, 5R11, 5R17, 5R16, 5R18 and 5R19to battery SBZ. The'windings of the six relays 7TSO-5 are, in thismanner, respectively connected through the normal armatures 1 of six ofthe slow release relays 5SRO9. The windings of relays 7TS4 and 7TS5 arealways connected through 4the normal armatures l of relays SSRS and5SR9, and the windings of the other four relays 7TSO-3 are connectedthrough armatures 1 of four of the relays 5SRO-7. The operation of thevertical group relays 6VGO-11 determines which four of the relays 5SRO-7are to be utilized. As indicatedin Fig. 6, Figs. l1 and l2 illustratethe connections to the armatures of relays 6VG1-10. Fig. ll, forexample, illustrates that the winding of relay 7TSO is connected toarmature 1 of relay 6VGO.

There are ten sets of slow release relays 5SRO-9. The sets of relays5SRO-9 are individually associated with ten crossbar switches SCRO-9, ofwhich, only switch 5CRO is sho-wn. The operation of relays 6H0-9determines which one of the crossbar switches 5CRO-9 is to be utilizedto service -the call. The relays 5SRO9 are normal when the associatedtrunks 5T0-9 are idle because trunks STO-9 are connected to theverticals of the switch SCRO. If trunk STO, for example, is busy, thehold magnet 5HMO is operated, and -a path is completed through theoperated armature 1 of relay SHM() for the relay 5SRO. With the relaySSRi) operated, the operating path for the trunk selecting relay 7TSOthrough its armature 1 is not completed. In this manner the trunkselecting relays 7TSO-5 .are operated, upon the operation of relay 6TC,only if the associated ones o-f the trunks 5T09 are idle. With alltrunks STD-9 idle, as described above, all sixtrunk selecting relays7TSO-5 are operated.

When ground is con;`

epesses There are ten relays SRO-9 that are utilized and only six relays7TSO-5. The `armatures 1 of relays 5SRO-9 that are not connected to thewindings of 4one of the relays 7TSO-5 are connected to one of the fourresistors 6E through 6H. The resistors 6E-H terminate the connectionsfrom the -four non-used armatures 1 of relays 5SRO 9. Fig. 11illustrates the connections of resistors 6E-Hto the `armatures `ofrelays VGtl-ll, and Fig. 12 illustrates the connections from thearmatures of relays 6VGO-11 to lthe armatures of relays 6H0-9. Theresistors 6E-6H function as locking paths for the four non-used ones ofrelays 5SRO-9. The paths through the windings of relays 6TSO-5 functionas locking paths for the lother six of relays 5SRO-9. The locking pathsare utilized during the trunk selection operation to prevent the releaseof any operated ones of relays 5SRO-9 until the trunk selectionoperation is completed. When one of the hold magnets 5HMO-9 is released,the associated one of relays 5SRO-9, therefore, remains operated duringthe trunk selecting operation.

As described above, the windingsl of relays 7TSO5 are connected througharmatures of six of the ten relays 5SRO-9, which are associatedindividually with the trunks STO-9. The six associated ones of the tentrunks STO-9 are referred to as being in the same multiple., At the lineconcentrator 110, the calling line 4L04 is connectable to any one of thesix trunks in the multiple but not to the lother four. Fig. illustratesthe possible connections from line to trunk. For the line 4L04, forexample, a connection may be established to any one of trunks ST1, ST6,STO, 5T7, ST8 and ST9. A connection cannot be established from line 4L04to -any one of trunks ST2, ST3, ST4 and ST5.

If all six trunks of the multiple are idle, all six relays 7TSO-S areoperated. The relays 6VGO-11 elfectively determine the multiple at thecentral oice just as the rline circuit connections do, as is hereinafterdescribed, at the concentrator 110. lIt is necessary, of course, for themultiple at each end to be the same.

When any one of the relays 7TSO-5 operates, it opens the operating paththrough its normal armature 1 for therelay 6TC, causing 'it to release.When the relay GTC releases, it, in turn, releases all except one of therelays 7TSO-5. Thevoperated one of the relays 7TSO5, which has thelowest designation, remains operated and the others release. When allsix relays 7TSO-5 were operated, the release of relay 6TC, in turn,releases the relays 7TS1-5, with the relay 7TSO remaining operated. Therelay 7l`S0 is locked to battery 7B2 through its operated armature 1 andthe operated armature 1 of relay 7D. -In this manner when relay 6TCreleases, only one of the six trunk selecting relays 7TSO-5 remainsoperated.

The relays 7TSO-S provide for the preference selection 0f the six trunksconnectable to the calling line. When relay 7TSO is operated, itindicates that the preferred trunk connectable to the calling line isidle and that a connection is to be established thereto.A When the callis initiated at the subscriber line 4L04, the preferred trunk is STO asshown in Fig. 10 and mentioned above. In the preference column-in Fig.l0, the preference of trunks is from left to right. For line 4L04 thetrunk preference is 0, 1, 7, 6, 8, 9.

When relay 7TSO operates, it provides a service ob servation indicationto the circuit 801 by completing the readied path, described above,through lead 802. The indicating path is from ground through resistor7S0, the operated armature 0 of relay 7TSO, the armature of switch 8A,terminal L of switch 8A, the right operated armature of relay 3VFT4,cable 8C2, -terminal 4 of switch SVF, the armatures of switches SVF andSVG, terminal 0 of switch SVG, cable 8C1, the operated right armature ofrelay 3VGTO, the operated armature 3 of relay ZHGt), cable SC3, terminal0 of switch SHG, the armature of switch SHG, lead 802 and the ring leadof trunk 8T to the circuit 801. In the circuit 801, the groundconnection energizes an indicator, not shown, to which the obf`servation operator responds. The operator establishes a connection inthe circuit Sill to the trunk 8T. The other end of the trunk 8T, asdescribed above, is connected by the switches StlZ and S61 to the trunkSTO. The operation of relay 7TStl, in this manner, indicates theselection of the preferred trunk STO, and provides an indication thereofto signal the observation operator. If relay 7TSO is not operated, theoperator is not signaled. Observation is therefore not provided for allcalls originating at line 4L04 but only for those for which thepreferred trunk STO is selected.

The routine observation is provided only for originating calls becausethe signaling path to circuit 801 includes armatures on. the registerrelays ZHGD, 3VFT4 and SVGT which are only operated for originatingcalls. By utilizing armatures on relays 65H0, `6VGtl and 7VF4 instead ofrelays ZHGtLfSVGT() and 3VFT4 observation could be provided forterminating calls as well as for originating calls if so desired.

Relay 7TSO is operated to signal the observation operat'or before aconnection is extended from either end of trunk STO. The observationoperator can observe the operation of the concentrator to collect line4L04 to trunk STO, and to observe the operation of switch SCRt) toIwhich the central oiice end of trunk STO is connected.

During the trunk selecting sequence of operations, the marker 700'selects an idle connection from the trunk frame, noty shown, to ahorizontal of the crossbar switch 5CRO. The utilization of the switches5CR-9 allows for the trunk multiple connections where less than all thetrunks 5T0-9 are connectable to each subscriber line. If trunk multipleswere utilized, and the trunks 5Ttl9 connected directly to thehorizontals instead of the verticals of switches 5CRt-9, the marker 760may select a horizontal that is not connectable to the calling line. Theswitches 5C80-9 allow for the connection of each horizontal to any oneof the trunks, so that independent of the selected horizontal, thepreferred idle trunk, in the trunk multiple connected to the callingline, is utilized.

If the tenth, or bottom, horizontal of switch SCR() is selected, theline line connector 701 provides an operating potential through thecable 7C3 to the winding ofthe select magnet 5SM9 causing it to operate.With only one of the trunk selecting relays 7TSO-5 operated, whentheselect` magnet 5SM9 is operated, an operating path is provided forthe test check relay 7TSK. The operating path for relay 7TSK is fromground through the op# erated armature of the select magnet 5SM9, thenormal armature 11 of relay 6TC, the operated armature 2 of relay 7TSO,the serially connected normal armatures 3 of relays 7TS1-5 'and thewinding of relay 7TSK to battery 7B3. Relay 7TSK, in this manner,operates only after the completion of the selection of the preferredidle one of trunks STO-9 by the relays 7TSO-5, and upon the operation ofone of the select magnets 5SMO-9.

When relay 7TSK operates, it causes the pulse generator ZPG to supplymark pulses to the concentrator 110 and it provides a connect potentialto the tip of the select trunk STO.

When relay 7TSK operates, it connects ground to the mark terminal of thepulse generator ZPG. When the pulse generator ZPG receives the markground potential, due to the operation of the relay 7TSK, it initiates amarking operation for readying the six trunks in the multiple -connectedto the calling line 4L04. A series of mark pulses are supplied fromgenerator ZPG through amplifier 2ML and resistor 2R9 to the lowerprimary of transformer 2T1. The lower primary of transformer 2T1 isconnected to battery ZBS and to varistor 2V2. The secondary oftransformer 2T1 is connected through the control pair 1CP3 totransformer 1T6 in the co-ncenrator 110. The upper primary oftransformer 1T6 is connected through resisto-r 1K3 to the amplifier lMK.The output of amplifier IMK is connected to the input terminal 1 ofY theflip-Hop circuit 1M, which is similar to the circuit 2HGTO describedabove. The circuit 1M isset by the tirst mark pulse from the centralotrce. When the circuit 1M Lis set, it operates relay lMR, the Vwindingof which is connected to battery 131. When relay IMR operates, itconnects battery 1B1 through its operated armature to the windings ofrelays 1m30-4 and IVGtB-l. The Iwindings of relays 1VFii- 4 areconnected, respectively, through varistors 1V0-4 to the output terminals2 of the stages in counter Ilv'l-T. The lwindings of relays 1VGO-11 areconnected, respectively, through varistors 1V10-21 to the outputterminals 2 of the stages in counter IVG. Since, as described above, thepulse sourceZPG outpulsed, or supplied, to the concentrator 110 a numberof Vertical group and vertical le pulses which indicate the identity ofthe calling line, the counters IVF and -1VG are set in accordancetherewith. -When the calling line is line 4MM, the last stage in counterIVF and the first stage in counter lVG are set. When a stage is set a 2volt potential is at the associated terminal 2.- 4With the first stagein counter 1VG and the last stage in counter ,1X/F set, when relay IMRoperates, it causes the operation ofvrelays lVGt and VFt.

With one of the relays 1VFO-4 operated, and one of the relays lVGtD-loperated a -65 voltvsource 1B2 is connected to one of the 60 linecircuits 4LU 00, 59. There is one line circuit for each of thesubscriber Vlines 4MM-59, but only the circuit 4LU04 is shown. With thecounters lVF and lVG set at the Videntity of the calling line, the markpulses are` effective to select the line circuit which is individual tothe calling line. Each of the line circuits 4LUOt-59 hasfsixcrossponts,or line units, 4U0-5 which are connected tothe associatedrsubscriberline. The 60 sets of line units 4110-5 ,provide for connections betweenthe 60 lines 4MM-,59 andthe ten trunks STG-9. With only six line kunitsfor each line, each line is connecta'ble `to only six of the `ten-trunks 5T9-9. Fig. 10 illustrates the connections fromlthe line units4U0-5, in each of the circuits .4LU00 -S9, to Athe trunk circuits ATG-9which aIeindiViduaHy associated with the trunks STG-9. As shown inFig.10'. the,sub scriber lines, which are in the same vertical group, .areconnectable to the same six trunks. For examplethe tive lines LUG-4,which are in the vertical group. 0, are connectable to the trunks ST1,ST6, STO, ST7, ST8 .and ST9. As described above, the trunkswhichareutilized for a vertical group .are vreferredto as a multiple'.All twelve multiples are dierent in order to distribute the load carriedby any one trunk. Such a distribution system of multiples is referred toa slip multiple. The lines ELM-59 are connectable to the trunks STO-9 ona slip multiple basis.

As shown in the line unit 4U0, each of the line units 4U0-S includes aserially connected relay 4C() and. gas tube 4CT. When the relay 4C() isoperated, a connection is provided from the associated line to one ofthe trunks STO-9. When the relays 1VF4 and IVG@ are operated, 'asdescribed above, the -65 volt battery 1B2 is .connected to the linecircuit 4LU04. The battery 1B2 is connected through the operatedarmature of relay 1VF4, and the operated armature 4 of relay IVG() tothe windings of the six relays 4C0 in the circuit tLUttft. The

anode of. the gas tube 4CT in'each of the units 4U0-5 is connected toone .of the trunk circuits 4T0-9. The connection from the `anode of atube 4CT is through a varistor 4D3, and resistor. ARS, to the ring tipof the associated one of trunks STG-9. For example, as indicated in Fig.10,.the gas tube 4CT, shown in the line unit tUti .of circuit 4LU64, isconnectedthrough the circuit 4T1 to the trunk ST1. The tube 4CT doesnotionize and the. associated relay 4Gb does not operate until apositive connect potential is provided onthe tip of the trunk ST1connected thereto.

When relay Y'7TSK is operated it provides, as briefly mentioned above, aconnect potential to the tiplead'of the selected trunk.A Morespecifically, when relay 7TSK 16 operates, a connection is, providedfrom the volt battery 7137y through the normal armature 2 of relay 7LB,`the operated armature 7 otl relay 7TSK, theoperated armature 4 of relay7TSti, the operated armature 14 of relay jVGil, the operated armature C0of relay Htl, the no rmal armature 2 of the relay 5SRO` and the normalarmature 2 of the hold magnet SHMO to the tip llead ofthe trunk`5T0. Thetrunk 5T0'is connected by the trunk circuit 4T@ to the line unit 4U2 incircuit 4LU04. [Thetip lead of trunk STO is connected through resistor 35 and varistor 3D3 to the'vanode of tube 4CT of unit 4U2 in circuitALUM. The connect potential is alsoprovided from circuit 4T0 to lineunits in some of the other circuits 4LUtlil-3, 4LU05-09, 4LU25.-129,4LU35`-44 and 4LU50-54. The other circuits, however, have not beenmarked, or connected, to the I-65 volt battery I1132. vThe combinationof the 65 volts atthe cathode of the tube ACT, and the +100 volts attheanodel lof the tube 4CTin unitl 4U2 of'circuit 4LU04, causes theionization of the tubex 4CT. When the tube 4CT ionizes, relay 4C@operates to establish a connection through the crosspoint 4U2/trom thecalling line 4L04'to the selected trunk STO. 'i

When the crosspoint U2 of circuit 4LU04 is closed, the markpulses, whichare still being supplied'from generator ZPG, areV returned as line busypuls'sthrough the controlpairs lCPl-E vto the central oi'ce. f v/Thenrelay dCi) operates, it forward-biases a diode 4M2 in circuit 4T@ toallow for the passage Vof 'the mark pulses. The dio-de 4M2 is normallyreversed-biased by the` battery 4134, which is connected thereto'through the resistor .41.1, ,varistorV lRV and resistor 4B. v The otherterminal of varistor MZ is connected Ato ground through the resistor 4M,and to the output of the' amplifier IMK through the capacitor 4C1.',When relay 4C() operates, itfextends the connection from the -65` voltbattery 1B2`through the operated` armature 4 of4`relay 4C0, varistor`.4RV and resistor'4L1 tothe battery 4134 locking `relay 4C@ operated.The current through resistor 4L1 causes the potential at varistor 4M2 toYdecrease `to allow the passage of mark pulses. With the varistor45M2`forward-biased, the succeeding mark pulses from the central oflceare supplied'through the amplier IMK, the capacitor 4C1, Vvaristor 4M2and capacitor 2CD tothe line busy amplifier LB. V1n this Vmanner thesucceeding niark pulses are routed back to thecentral ofticethrough theamplier 1LB` as line busy pulses to indicate ythat the crosspoint relay4C0 has operated. Battery ABS in circuit 4T() is connected through the'inductor `EBTand the operatedarmature 3 of reiayv4C0 in unit 4U2 toreverse-bias the varistor 4D; When 'scanning is resumed, the kline 4L04does not' initiate a service request when it is connected to one of thetrunks STG-9. The scanning pulse from counter IVF is then directedthrough capacitor t/F, varistor 4D, capacitor 4C,"the operated armature3 of relay; 4Gb, and Vvaristor 4M1 to the amplierlLB.

At the central oHice, the converted mark Vpulses are provided lthroughthe amplifier ELBL, the open gate SLBT to the input terminal 1 oftheflip-oplcircuit 5LB. When the ip-tlop circuit 5LB is set, it causes theoperation of the line busy relay 7LB which provides the crosspointclosure indication to the marker 700 by completing a path from one ofthe leads LH to the hold magnet Sl-IM() and removes the +100 voltpotential from the tip lead of trunk STO. The line hold leads' LH are`multipled through the'operated armatures 2 of the relays 7VFO-t. In theillustrative example, with line ALM initiating the service request, theground potential' is provided through the operated armature 2 of relay7VF4, the operated armature 1 of relay 7LB, the operated armature 3 ofrelay 7TSil, the operated armature 9 ot relay 6VGO, the operatedarmature 12 of relay 6H!) to'the winding of the hold magnet rSHMO whichis v connected to the battery 5B1. When the marker 700 receives the 17crosspoint closurev indication, it supplies a ground potentialthrou'ghthe line hold leads LH to operate the hold magnet HMO. When the holdmagnet 5HMO operates, it closes a connection between the trunk STO andthe bottom, or tenth, horizontal of the crossbarswitch SCRl).

`When the hold magnetSHMt) operates, it also opens the path to the +100volt connect potential, through its vnormal armature 2 VVfrom the tipring of the trunk STO,

the relays`7TSO-'Sis operated.

When the marker Y'700 has operated ythe'ho'ldV magnet 5HMO and completeda connection from the calling line -4L04 throughtrunkl`5T0 and switchSCRO to an .originating callregister, nowshown, it initiates the releaseof the connector701. 'When the connector 701 releases it in turn allowsthe relays 6H0, 6VGO, 7D.and 7VF4 to release. When relays 6H() and 6VGOrelease, they in :turn cause the release of -relay k7TS0 and openthesignal path through lead 802 to circuit 801. lWhen therelay 71`S0releasesitin turn causes .the lrelease-.of the relay 7TSK. vWhen relay7TSK releases it .closes the gate -5LBT, resets the -ip-op circuit 5LB.and .restarts `the generator 2PG. The battery 7B6.is connected, .upon

the .'releaseof relay A.'TTSK, to reset thelip-op circuit 5LB,to-r'esetthe tlipopcircuit 2HGTO, and torestart the normal scanningofthe, pulse generator ZPG. Relay y "7L-.Bis released whenV circuit SLBisreset, andrelayZHGll is released when circuit 2HGTO `is reset. Whenrelay ZHGO lreleases, it in y.turn `releases relays 3VFT4 and 3VGT0.`

When :the source yZPG is restarted it first supplies a resettpulsetotheline conCentrator-and toregister 300. The vamplifier flRS,whichreceives thereset-pulse in the concentrator 110, Vis connected, asdescribed above, to the circuitlM. The-reset` pulse is supplied throughthe amplierlRS, the capacitor 1C2 and varistor .v1-D7 t0 the resetterminal 3 of the flip-flop circuit -1M, causing kit to reset.

When-circuit-1M resets, it releases relay lMR, which, -in turn, releasesrelays --1VF4fand -1VGO. Relay 4C0, however, remains operated-duetothelocking pathithroughits operated armature 4. `The1ocking path is frombatteryvf4B4, through resistor 4L1, varistor 4RV, the operated armature4-oflrelay 4C0, lthe winding of relay 4C0, and resistor 4CT1 to'ground.

As described above, when the hold magnet SHMt) is yoperated the +100voltvconnectfpotential is removed from the tip leadof the selected trunkSTO. With the connect potential removed, tube KtCT extinguishes butrelay 4C0 remains-operated over thelocking path-to battery 4B4.

The normal scanning cycle continues until lanother service requestis-made by one ofthe lines 4L00-59, or acall is made thereto.Normal'scanning continues -during call back and disconnect. Call backis'a sequence of operation for establishing a connection to anjoutgoingtrunk which occurs after dialing-is completed. The callback sequence ofoperation is ldescribed in the aboveidentied disclosure ofJoel-Krom-Posin. Briefly, the originating'regi'ster, notshown, whichreceives the dial pulses, calls in the marker 701). The marker-700releases switch 5CRO and then lestablishes a connection through switchSCRO from trunk STO to an outgoing trunk, notshown. The connectionfromthe calling line 4L04-to trunk 'STO remains locked during call back.Since the same trunk STO is utilized `for call back, `the tube llDTionizes.

'l 8 observation operator can continue the observation through thecall-back sequence.

When the subscriber at substation 4S04 hangs up, the opening of line4L04 is detected at the central oice, and magnet 5SH-M0 is reieased.When the magnet SHM() releases, a -130 volt-disconnect potential isapplied to the tip lead ofthe trunk IST0 and the slow release relaySSR() is released. The disconnect potential isprovided from batteryB'D-throu'gh lthe normal armature 11 of relay 6H0, the still operatedarmature 2of slow release relay SSRtl, the normal armature V2 of relaymagnet SHMt), the tip lead of trunk`5T0, resistor 4K5, and varistor 4D?.to thercathode .of tube 4DT. The anode of tube 4DT is connected throughresistor 4L1 to battery 4B4 so that When tube 4DT ionizes, vits anodevpotential becomes Ar'nore negative, and reverse-biases the varistor tRVto open the locking path for relay 4C0. Whenrelay 4C0 releases, itdisconnects line 4L04'from trunk STO. rWhen relay ASSR`0tinally-releases, the disconnect potential is removed from the tipleadof trunk STO. During the disconnect sequence the normal scanning cycleis continued. The observation operator may remain 'on trunk 8T if sodesired through the conversation interval and disconnect as well as callback if so desired. The entire call lfrom start to nish may in thisvmanner be observed.

RoutineI observation `.on fa predetermined :trunk For routineobservation of one of A.the trunks 5T0-9 of one of theconc'entrators'110419,the service observation control 810 is set toselect vthe concentrator and the trunk connected to the concentrator andthe yswitches 501 and S02- a're operated to connect the trunk 8T to theconcentrator trunk. If, forexample, the observed trunk is vtrunk 'STO ofconcentrator 110, lthe selector switches tA-I are set -at the 0 terminalandthe switch -8HG is set at the 0 terminal. The line selector switchesSVF and SVG are not utilized, and the switches 502 and S01 are set tokconnect trunk 8T to trunk STO. With the-service observing control 810set, in this manner, whenever the trunkSTtl is selected for a calloriginatingfat any y -ST3,'STO, ST8 and ST9 are connectable vto thecalling line 4LOS. When any one of the relays 7TSO-S is operated duringthe trunk selecting sequence of operations, its operation indicates theselection of one of the six trunks. VWhen the trunk STO is :selectedasignaling path is completed through the selector switches SA-I totheservice observing circuit S01. ,The -wiring between the selectorswitches 8A-I and the right armatures of relays 3VGTO11 includesessentially thetrunk multipling information. For line 4L05, trunk STO isselected as a fourth preference, that is, trunk STO is selected only iftrunks ST4, ST7 and ST3 are busy. With trunks ST4, ST;7 and ST3 busy,relays 7TSO, 7TS'1 and 7TS2 are not operated during the trunkselectionsequence of operations. Relays '7TS3, 7TS4 and 7TSS, however,operate. The relay 7TS3 is locked operated and relays 7TS4 and /TSSrelease. As described above, with only one ofthe relays r7'l`S0-5operated, the relay '7TSK is operated. When relay 'ITSK operates, itconnects resistor 750 through its operated armature 0, the operatedarmature 0 of relay TISS, the armature of switch 8G, contact 0 of switch8G, the lead 1l through cable SCL the right operated armature of relay3VGT1, the operated armature 3 of relay 2HGO, the terminal 0 of switchSHG, the armature of switch SHG, lead 802 and the ring lead of trunk 8Tto the service observing circuit 801. It is only when trunk YST0 isselected for line `4L0S that a service observation signal is provided tothe service observing

